Abaixo está uma instrução que descreve uma tarefa de geração de SQL, combinada com uma entrada que fornece mais contexto sobre os esquemas de tabela disponíveis. Escreva o código SQL que responda adequadamente à solicitação
 ###Instrução: Qual ano teve playoffs de campeão?
 ###Tabelas: CREATE TABLE varsity_letter_winners (varsity_letter_winners_id AUTO_INCREMENT PRIMARY KEY, Player VARCHAR, Position VARCHAR, Games started VARCHAR, Hometown VARCHAR, Height VARCHAR, Weight INT, Class VARCHAR, Previous experience VARCHAR) CREATE TABLE liga_acb (liga_acb_id AUTO_INCREMENT PRIMARY KEY, Game INT, Date VARCHAR, Team VARCHAR, Score VARCHAR, High points VARCHAR, High rebounds VARCHAR, High assists VARCHAR, Location Attendance VARCHAR, Record VARCHAR) CREATE TABLE year-by-year (year-by-year_id AUTO_INCREMENT PRIMARY KEY, Year INT, Division VARCHAR, League VARCHAR, Reg. Season VARCHAR, Playoffs VARCHAR, Open Cup VARCHAR) CREATE TABLE tallest_proposed (tallest_proposed_id AUTO_INCREMENT PRIMARY KEY, Rank INT, Name VARCHAR, Location VARCHAR, Height feet / metres VARCHAR, Floors VARCHAR, Year Proposed VARCHAR) CREATE TABLE locomotives_withdrawn_from_service (locomotives_withdrawn_from_service_id AUTO_INCREMENT PRIMARY KEY, 'Name' or designation VARCHAR, Wheel arrangement VARCHAR, Builder VARCHAR, Year built VARCHAR, Year withdrawn VARCHAR)  
SELECT AVG Year FROM year-by-year WHERE Playoffs = champion